Re: Codd's Information Principle

On Nov 6, 5:08 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> Tegiri Nenashi wrote:
>
> ...
>
> > Likewise, relational calculus quantified expression
>
> > exists y : R(x,y)
>
> > is essentially a disjunction
>
> > R(x,1) <OR> R(x,2) <OR> R(x,3) <OR> ...
> > ...
>
> In the spirit of the recent precision, it doesn't look to me like
> 'R(x,1)' et cetera are sets of tuples, which I believe '<OR>' requires.
>   Shouldn't that '<OR>' be logical 'OR'? Also the result doesn't look
> 'truth-valued', shouldn't it?

 'R(x,1)' is a result of substituting y=1 into R(x,y). This is literally the same trick as substituting n=1 in the term x^(-n) which is a part of summation

sigma( n={1...inf} , x^(-n) )

We simply substituted sigma with "exists", bind variable n with y, and left x as free variable in both cases. Moreover, many math books use the big disjunction symbol "\/" for "exists" in order to emphasize the idea that existential quantification is merely repeated application of binary disjunction. Received on Sat Nov 07 2009 - 03:37:43 CET